1. Field of the Invention
The present invention relates to an airless tire which absorbs shock and holds pressure applied to the tire through an auxetic spoke buffer without using air pressure.
2. Description of the Related Art
While a vehicle is running, tires receive substantial pressure due to the weight of the vehicle, passengers, freight, and the like. Thus, tires are formed to endure such pressure, to provide a buffering function by absorbing shock which can be applied from the road to the vehicle, and to maintain a proper shape so as not to cause any problem when driving the vehicle under such pressure and impact.
Tires having such structure are applied to most vehicles, such as automobiles, bicycles, rickshaws, tractors, and the like.
In order to endure exerted pressure and provide a buffering function while maintaining a proper shape, pneumatic tires filled with air are mostly used.
Such pneumatic tires have substantially different operations and effects depending on the pressure of air in the tires, and cannot maintain a proper shape when the tires have a puncture, thereby causing difficulties in vehicle driving and reduction in lifetime of the tires.
In particular, the most serious problem of air-filled tires is a puncturing phenomenon that a hole is punched in an air filled space of a pneumatic tire and causes the air filled space not to properly work. The puncturing phenomenon occurs during drive of a vehicle and causes a traffic accident.
In order to solve the problems of air-filled tires, an airless tire is under development and various forms of conventional airless tires have been suggested.
Initially, airless tires could be used under conditions in which the tires receive small load as in the case of bicycles, and were produced by molding rubbers or synthetic resins having excellent durability and restoring force into a tire shape.
With remarkable advances in airless tire technology, an airless tire which can be used for a vehicle is developed. Most airless tires to be used for a vehicle have a honeycomb-shaped spoke buffer 300 (see FIG. 1), as disclosed in U.S. Pat. No. 5,494,090, U.S. Pat. No. 7,143,797, Korean Patent Application No. 10-1990-0015355, and PCT/US2008/058308 (WO/2008/118983).
That is, an airless tire is a non-pneumatic airless tire which has a cylindrical tread to be brought into contact with the ground, an axle fixing section having a smaller circumference than the tread and disposed inside the tread, and a honeycomb-shaped spoke buffer connecting the tread and the axle fixing section and providing a buffering function.
However, a conventional airless tire having the honeycomb-shaped spoke buffer 300, as shown in FIG. 1, can be excessively transformed into a shape having difficulty properly performing essential functions of the tire, for example, a shape having an excessively widened ground contacting surface, when the spoke buffer 300 is transformed (generally into an irregular shape) by pressure or impact. Further, the spoke buffer does not rapidly return to an original shape when pressure is removed.
Further, since the spoke buffer 300 has a short lifespan for functioning properly, the airless tire also has a short lifespan.